Wood impregnating and coloring process



Jan. 6, 1959 w. H. BRAUN, JR 2,867,543

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United States Patent WOOD IMPREGNATING AND COLORING PROCESS William H. Braun, Jr.North,HollyWood, Calif., assignor to Western Sealant Development Corporation, Culver City, Calif., a corporation of California Application October 22, 1956, Serial No. 617,224

14 Claims. (Cl.117'-46) like structure extending into the pores of the` wood and' coating its surfaces, `and giving the wood greatly increased strength and hardness. This increased strength andV hardness, together with the above discussed'controlled'change in appearance, render it". possible `to utilize soft woods, such as pine, lir, spruce and redwood, etc., for purposes ordinarily requiring expensive hard woods.` The `use of such soft woods in the place of hard' woodshas. the obvious advantage 'of reducingcosts, and also greatly. simplies the process of machiningA orshaping the Wood', for

example in making furniture, since the soft Woods can be shaped very easily prior to impregnation, and canthen be readily -convertedto an altered very hard and strong state by Athe Vimpregnation process. After, the impregnation, the surface of the wood may be sanded or otherwise worked, and requires no Varnishing or other surface coating lay-reason of thek presence of. thel plastic rin; the;` Y

wood.

In addition to increasing the strength and hardness of the Wood, the present process also renders the-,composite Wood and plastic structure much moreuniformthrough--V out, since the plastic very effectively lls in all cracks, crevices, and other voids in the wood; Further, the treatment increases, by approximately ten times, the resistance'ofthe wood to water absorption, andY also considerably increases the resistance totre, chemical attack,-

and othertypes of damage or deterioration.

The present invention is incertain respects particularly concerned lwith the control of the process in a mannerv to darken the color of the vwood duringthe process, so that an Vinitially light-colored andV inexpensive wood may have the appearance of a dark and normally veryrare, expensive wood.y Forl instance, a low-cost, light-'colored wood may be given the-appearance, as well yas the physical characteristics, of such woods as ebony, teakwood,

' ironwood, and the like. In addition, the process may be very easily regulated to produce any intermediate shade of'wood between the very lightest and the very darkest to thereby produce various attractive appearances not hitherto known, and to accomplishall of these different appearances without changes in the resinous materialv being usedr as an impregnant. Thus, a single batch of resin may be employedfor forming impregnatedjwoods of various different colors at will, with the resultthat ai commercial application of the invention can," withoutuntremely" attractive.-

ICC

due expense, be extremely exible as. to the type and colorof product .being produced from a single impregnatingunit.`

To attain such colorcontrol, the process is designed to actually change the color of the Wood itself, as distinguished from the resinwhich impregnates the wood.'

The resin'is then so chosen as to be light-passingin character, so that the changed color or .shade of the woody is visible through the resin. Preferably, the cured resin is transparent or clear, and desirably `substantially colorless, to allow viewing through the resin .of the darkened grain .structure-and highlights of the wood, with` the result that the, overall appearance of theV wood may be ex- If desired, in orderv to achieve a particular eiiect, the` cured resin may, in some cases, be translucent rather than transparent.

In accordance with the invention, the change in color ofthe wood-,is effectedby heating the wood toA an, extent (at a temperatureJand `for. atime) sufcient to visibly andl considerably darken thefcolor of the wood by virtue of,.t,he internal, reactions whichloccur inthe wood as a result offthe heating., It` is, of course, virtually impossible to deiner exactly what` typesof reactions` produce this darkeningaction,V butfor presentpurposes, it will sulice. tovsay, merely that *the heat appears Vto cause changesy in. the organic materials-in, the Ywoodwhich. visibly change the color of the wood. Toproduce avisible-changein. the wood color, thev heat must be considerablygreater than thatnormally utilized andVH required for curing.of thefl` resin., Thev extentV toV which. the `wood 'is darkenedmay, be. controlled by regulating, the amount. ofv 'heat towhich lA the wood is' subjected," so that,-the-fwood. maybegix/en.

eitherv a light brownor. tan-V appearance, or. a` dark,l almost black',

shade. Y Y

The heat and the temperature towhich thewood is subjected-should,` at a, minimum, beat least: enoughltolvisibly, darken the wood, and should, at a maximum be less than..

the, utemperature vand heat which would .break down/or damagethe `resin being used,` and l less thanA th'ehar,v point. of" the resulting composite wood and resi11.pr0duct.f.Tof

makea commercially practical operation;` thetemperature for `darken'ingnthe wood is .preferably at leastaboutS() F., and 'preferably not greater than about,475 f The optimumv temperatures .forzcertain speciiicl woods. areas follows.:

When the temperatures .arewithin therange of 3.50? F.to"475" F., the darkeningof'the Woodjrnay be produced Within commercially practicable` time periods,I

usually between aboutl/zj hour and 2 hours.

For. best'results, Iftindit m'ovstjdesirable, in performing the process,to rstevacuate .allgair and volatile nia-` terialsfrom the poresof they wood, then to. impregnate Y.

the uncured'resininto the 'pores' of the wood,"then to cure the resin,(usu,ally by heat), andi then tok further heat the wood and resin `to an" extentA visibly` darkening the `color ofithe former but not damagingrthe resin (preferably at a temperature between'SO,J TF',` and 475 F; as .dis-

cussed).

As mentionedabovgthe wood is preferably soptreated, i

prior to its actual impregnation, as to evacuate as much as possible ofthe air and volatile constituents. f1"om,theV

Patented Jan. 6, 1959,

appearance, for anyintermediate, appearance ory um, usually amounting to an absolute pressure of less than 30mm. Hg, (preferably under 5 mm. Hg). evacuation may lbe further enhanced by maintaining `the wood at an elevated temperature during its subjection t the vacuum, the temperature typically being at least about 120 F. but under the kindling temperature of the wood,

Thev,

and preferably. beingbetween about 200 and 350? F. t

(optimum about 250 13.).r t

'After the air and volatile constituentshave thusfbeen driven out of the pores in the wood, the uncuredr'esin in liquid form may then be forced`by pressure into those pores to deeply impregnate the wood. Such impregnation may be effected by completely` immersing the Wood in'. a body ofthe liquid' resin, land then subjecting 'the resin to superatmospheric pressurerto'iforce it into the wood.` Thelpressure may be labout 100 p.A s. i., and may -be alternately applied and'relieved through one or more cycles (normally 2 to 5 cycles), to effecta'more'thorough" impregnation thancan `be attainedby 'a single applicaj tion ofV pressure. Between the pressureperiods, the pressure of the resin and therefore of the, wood may bevreduced only to atmospheric pressure, or may' actually bes,

reduced to a vacuum, say as lowas Vz p.f s. i. absolute, and preferably less than 5 mm. Hg. Apparently, this alternate application of superatmospheric and then subatmospheric pressure lacts to first force theresin partially into the wood, and then to allow small amounts of re- .tained air and gases to bubble out through the resin (while under vacuum), following which another pres-l sure surge forces the resin more deeply into the pores, etc. It has been found that in this way the'resin` can be forced into the pores of the wood through its entire' velopment Corp., 1008 W. 6th St., Los Angeles, Cali-` fornia.

(3) The phenol formaldehyde resin sold as ELL-3085 by Union Carbide & Carbon Corp., 2770 Leonis'Street, Vernon, California. t

(4) The urea formaldehyde resin sold as Uformite #700 by Rohm & Haas, 5657 Wilshire Boulevard, Los

Angeles, California.

The resin is, in some'cases, mixed with a`suitable diluent, such as styrene monomer or phenylglycidal ether, and

may contain an additive oradditives to increase its speed 'I of curing, or to giveother desired characteristics, certain typical additives being'b'enzoyl per0xide,'diethylene triamine or dodecylsuccinic acid anhydride.

Following the impregnation of the resin into the Wood,

the wood may be removed from the body of liquid resin within which it is immersed, and excess resin may be cleaned from its outer surface by a brush, squeegee, the

application of solvent, or any other suitable method. However, sutlicient resin is left'on the outer surfaces of the wood to form a'thin coating of resin on those surfaces as well as in the pores.

The next step is to cure the thermosetting resin, usually by baking in a suitable oven. The curing temperatureand time may be as prescribed by the manufacturer of the particular resin employed, butY for most resins (including those specifically Yenumerated above) a curing `temperature of 250 F. forone hour will be satisfactory. Thewood-darkening operation may be performed Yas a nalstep in the process, which, in some cases, may occur in its entirety after the curing of the resin has been completed. Inother cases, however, the darkening of 'the Wood may be commenced during the actual curing step itself, ifY the curing temperature is purposely made considerably higher than that normally prescribed for curing, and is sufliciently high to actually commence the darkening of the wood; that is, the temperature in the curing oven may, from the outset, be within the range previously prescribed for most effective darkening of the wood (350 F. to 475 F.), in which case the resin will very rapidly cure (say in about 30 minutes), with little or no darkening of the wood in thatshort period. After such curing, the continued heating of the wood and resin at this high temperature will produce a very readily visible and progressive darkening of the wood until a de- 1 sired shade has'been attained. If the initial curing is at la conventional relatively-low curing temperature, such as 250 F., the temperature mustbe raised after completion of the curing to a value such as that previously discussed which will .produce the desired visible color change.

The apparatus for performing the present process may be. completely conventional, and therefore will not be described in detail in this application. The 4initial evacuation and impregnation may be performed in a conventional autoclave, within which the wood may be placed,

and which can ii'rst be subjected to an internal vacuum, then be filled with resin through suitable piping, then be subjected to pressure and vacuum alternately to force the resin into the wood, and finally be drained to allow removal of the wood. The baking and heat treating can of course'be performed in any furnace capable of raising the wood and resin yto the specified temperatures.

-To assure the adequacy of the present disclosure, the

following typical examples are given of specific processes embodying the invention:

, Example 1 A piece of lwhite pine-measuring 4" x 6' x 1" was placed in an autoclave, andthe autoclave was then closed and sealed. A connected vacuum pump was then placed in operation to reduce the pressure in the autoclave and about the wood to 3. mm. Hg, and the/autoclave and wood were simultaneously heated to 120 F. After this pressure and temperature had been maintained for 1v hour, a liquid resin solution was admitted into the autoclave to a level completely immersing the wood, the l solution consisting of 128 parts polyester resin as sold by Western Sealant Development Corporation under the trade designation P. E. 1.

55 parts styrene monomer 1 part benzoyl peroxide The vacuum'was then relievedV and theresin solution was subjected to a pressure of p..s. i. for 60 minutes,

following which the pressure was reduced to a vacuum of 3 mm. Hg for l5 minutes and this cycle was then repeated 3 times to :force the liquid resin into the pores of the wood throughout its thickness. Next the resin was drained from the autoclave, and the wood was removed. The excess resin was cleaned from the outer surfaces of the wood by brushing, but leaving a thin layer over the entire surface of the Wood.V

Aftercleaning, the impregnated Wood was placed in an oven and heated for one hour at 250 F. and at atmospheric pressure to thoroughly cure the thermosetting resin. Following the curing period, the temperature was raised to 350 F. for a period of 1 hour, to darken the color of the wood to a golden brown color, without sub-' stantially affecting the transparent appearance of the resin. The product made in this way was hard, strong,v nre-resistant, chemical-resistant, water-resistant, and of a uniform darkened color throughout its thickness. It did not require varnshing or'other protection, and could be sanded or cut to any shape without affecting its surface color or nished appearance. y

Example 2 Same processas that of Example 1,:except for thefollowing variations;

(1) Fir wood instead of pineY (2) Composition of resinv solution 704 parts epoxy resin as soldY by Shell Development vCorporation under 'the trade designation Epon 828 32 parts phenyl glycidal ether 1 part diethylenetriamine 192 parts dodecylsuccinic acid anhydride (3) Curing temperature 300 F. for 45 minutes. (4) Temperature raised to 400 F. for 1A. hour after curing period to darken wood.

Example 3 Example 4 Same as Example 1, except temperature raised to 400 F. at commencement of curing and for 1 hour to first cure the resin at that temperature in about 30 minutes and then continue the heating after curing to darken the wood.

To facilitate an understanding of the present invention, there is submitted herewith a drawing, in which:

Fig. 1 is a fragmentary cross-sectional view taken through a piece of impregnated wood which has been formed in accordance with the invention; and

Fig. 2 is a flow-sheet representation of a preferred process embodying the invention.

In Fig. 1, the final product 10 includes a piece of wood represented at 11, and which is continuously coated along all of its outer surfaces by a layer of cured thermosetting resinous plastic material 12. This cured resin also extends deeply into the pores of the wood, preferably throughout its entire thickness. The wood has been darkened in color by heating, and the resin is of a light passingcharacter allowing viewing of the darkened color of the wood through outer resinous layer 12.

As represented in the flow sheet of Fig. 2, the first step in the preferred process may be to evacuate the pores of the wood, preferably by a combination of heat and subjection to vacuum. The next step is then to impregnate the wood with uncured thermosetting resin, following which the resin is cured as step three. Finally, the wood is darkened, as discussed in great detail above, by heating the wood after the curing step.

Iclaim:

l. The method of producing an impregnated darkened wooden member that comprises evacuating air and volatile constituents from the pores of a piece of wood by heating the wood and subjecting it to a vacuum, then immersing said wood in a body of uncured thermosetting resin in liquid form, applying pressure to said resin and thereby forcing the resin into the pores of the wood, removing said wood from the body of resin with some of the resin retained in the pores of the wood and coating the surface of the wood, heating said wood and carried resin and thereby curing the latter to a hardened polymerized form, and then continuing the heating of said wood and carried resin after the latter has been cured to said hardened form and for a time and at a temperature sucient to visibly darken the color of the wood by heat after said curing but not suicient to break down the cured resin,

. 6 v said cured resin being .transparent to allow the darkened grain of the wood to be visible therethrough.

2. The method of producing an impregnated darkened wooden member as recited Ain claim 1, including alternately applying pressure and vacuum Vto said body of resin while` the woodis immersed therein to thereby cause deep penetrationY of the resinl into the-Wood.

3. The method of producnganimpregnated darkened wooden'member as recited in claim 2, in which said darkening of the woodis` effected at a temperature between about 350 F. and 475 F.

4. The method of producing an impregnated darkened Wooden member that comprises impregnating a piece of wood with a thermosetting resin by forcing said thermosetting resin under superatmospheric pressure into the pores of the wood, curing said thermosetting resin to a hardened polymerized state after its impregnation into the wood, and heating said wood and resin after the resin has been hardened and for a time and at a temperature sufficient to visibly darken the color of the Wood by heat Iafter curing but not suicient to break down the hardened cured resin, said resin being of a lightpassing character allowing the darkened color of the wood to be visible therethrough.

5. The method of producing an impregnated darkened wooden member as recited in claim 4, in which said darkening of the wood by heat is effected at a temperature at least as high as high as about 350 F.

6. The' method of producing an impregnated darkened wooden member as recited in claim 4, in which said darkening of the wood by heat is effected at a temperature between about 350 F. and 475 F.

7. The method of producing an impregnated darkened wooden member as recited in claim 4, in which said wood is pine, and said darkening of the wood by heat is effected at a temperature between about 350 F. and 400 F.

8. The method of producing an impregnated darkened wooden member as recited in claim 4, in which said wood is fir, and said darkening of thev wood by heat is effected at a temperature between about 375 F. and 425 F.

9. The method of producing an impregnated darkened wooden member as recited in claim 4, in which said wood is birch, and said darkening of the wood by heat is effected at a temperature between about 380 F. and 430 F.

10. The method of producing an impregnated dark ened wooden member as recited in claim 4, in which said resin, after curing and after said darkening of the wood 'by heat, is transparent and thereby renders the grain of the darkened wood clearly visible through the resin.

1l. The method of producing an impregnated darkened wooden member as recited in claim 4, in which said thermosetting resin is cured by heating to a temperature which is superatmospheric but is less than the temperature subsequently used for darkening the wood.

12. The method of producing an impregnated darkened wooden member as recited in claim 4, in which said impregnation of the wood with said resin is effected by immersing the wood in a body of uncured resin, and applying said superatmospheric pressure to said body of the resin to force it into the pores of the wood.

13. The method of producing an impregnated darkened wooden member as recited in claim 4, including the step of evacuating air and Volatile constituents from the pores of the wood, prior to impregnation, by heating the wood and subjecting it to a vacuum.

14. The method of producing an impregnated darkened wooden member as recited in claim 4, including the step of evacuating air and volatile constituents from the pores of the Wood, prior to impregnation, by heating the wood and subjecting it to a vacuum, said impregnation of the wood with resin then being effected by immersing the wood in a body of uncured resin, and

applying said superatmospheric rpressure'to said body-of resin to forceit into .the pores of the Wood.`

References Cited in the le of this patent UNITED STATES PATENTS Kozelek Feb. 12, 1924 10 8 Snelling Aug. 6, 1929 Texier Sept. 24, 1929 Rice- Oct. 22, 1929 Booty et al. f'. Dec. 20, 1938 Kvalnes Apr.16, 1946 Stover Nov. 18, 1947 ABilhuber Nov. 14, 1950 Austin Apr. 8, 1952 Dannenberg Aug. 24, 1954 4McLaughlin Apr. 30, 1957 

1. THE METHOD OF PRODUCING AN IMPREGNATED DARKENED WOODEN MEMBER THAT COMPRISES EVACUATING AIR AND VOLATILE CONSTITUENTS FROM THE PORES OF A PIECE OF WOOD BY HEATING THE WOOD AND SUBJECTING IT TO A VACUUM, THEN IMMERSING SAID WOOD IN A BODY OF UNCURED THERMOSETTING RESIN IN LIQUID FORM, APPLYING PRESSURE TO SAID RESIN AND THEREBY FORCING THE RESIN INTO THE PORES OF THE WOOD, REMOVING SAID WOOD FROM THE BODY OF RESIN WITH SOME OF THE RESIN RETAINED IN THE PORES OF THE WOOD AND COATING THE SURFACE OF THE WOOD, HEATING SAID WOOD AND CARRIED RESIN AND THEREBY CURING THE LATTER TO A HARDENED POLYMERIZED FORM, 